1. Field of the Invention
The invention relates to a one-way clutch.
2. Description of the Related Art
A one-way clutch is used for various types of equipment (see, for example, Japanese Patent Application Publication No. 2013-257024 (JP 2013-257024 A)), by way of example, for an alternator in an automobile. A one-way clutch typically includes an inner ring 90, an outer ring 91, a plurality of rollers (engagement elements) 92, an annular cage 93, and springs 94, as shown in FIG. 5. The rollers are provided between the inner ring 90 and the outer ring 91. The cage 93 holds the rollers 92. The springs 94 bias the rollers 92. On an outer periphery of the inner ring 90, a plurality of cam surfaces 95 shaped like recesses is formed at regular intervals. A wedge-like space 100 is formed between each of the cam surfaces 95 and an inner peripheral surface 91a of the outer ring 91. One roller 92 is provided in each of the wedge-like spaces 100. A one-way clutch for an alternator is configured such that the outer ring 91 rotates integrally with a pulley. In FIG. 5, a rotating direction of the outer ring 91 is depicted by arrow R.
In the one-way clutch, when the rotational speed of the outer ring 91 is higher than the rotational speed of the inner ring 90 and the outer ring 91 rotates relative to the inner ring 90, each of the rollers 92 is engaged between the corresponding cam surface 95 and the outer ring 91. This makes the inner ring 90 and the outer ring 91 unable to rotate relative to each other. When the rotational speed of the outer ring 91 is lower than the rotational speed of the inner ring 90, the rollers 92 are disengaged from the inner ring 90 and the outer ring 91. This makes the inner ring 90 and the outer ring 91 rotatable relative to each other.
To allow the one-way clutch to function as described above, each roller 92 needs to be stably engaged between the corresponding cam surface 95 and the outer ring 91. Thus, the one-way clutch is configured such that, in each of the wedge-like spaces 100, the corresponding spring 94 pushes, with a predetermined force (elastic force), the corresponding roller 92 in a direction in which the wedge-like space 100 is narrowed.
An important factor that allows the spring 94 to push the roller 92 with the predetermined force is a circumferential positional relationship between each roller 92 (the cam surface 95 with which the roller 92 engages) and a corresponding one of cage bars 96 of the cage 93 to which the corresponding spring 94 is attached. In other words, when the distance (in other words, the interval) between each roller 92 (cam surface 95) and the corresponding cage bar 96 to which the corresponding spring 94 is attached significantly varies among the plurality of wedge-like spaces 100, a heavier load is imposed on some of the springs 94. As a result, these springs 94 fatigue, possibly shortening the life of the one-way clutch. A “spring area” as used herein refers to an area between each cage bar 96 and the corresponding roller 92 where the corresponding spring 94 is provided.
That is, a significant variation in the distance of the spring area (circumferential dimension) among the wedge-like spaces 100 causes a distance L between each roller 92 and a corresponding spring attachment portion 96a on the cage 93 (a side surface of the cage bar 96) to vary among the wedge-like spaces 100. Thus, in order to allow each spring 94 to push the corresponding roller 92 with the minimum needed force, the shape (length) of the spring 94 needs to be set, for all the spring areas, with reference to the case where the distance L is larger so as to allow the spring 94 to push the roller 92 with the needed force even in areas where the distance L is larger. However, in this case, the spring 94 pushes the roller 92 with a relatively strong force in areas where the distance L is shorter, leading to a heavy load on the spring 94 due to a reaction force. This may fatigue the springs 94 in these areas to shorten the life of the one-way clutch.
Thus, the variation in the distance L of the spring area needs to be reduced. To achieve this, a configuration has been proposed which allows the cage 93 to be fixed in position to the inner ring 90, on which the cam surfaces 95 are formed. Specifically, as depicted in FIG. 5, protruding portions 98 are formed on an inner periphery of an annular portion 97 of the cage 93, and recessed portions 99 are formed on an outer periphery of the inner ring 90. The protruding portions 98 are fitted in the respective recessed portions 99 to allow the cage 93 to be positioned with respect to the inner ring 90 and fixed thereto. Each of the recessed portions 99 is formed in an area different from the area of the cam surface 95, which is recessed so as to allow the roller 92 to engage with the cam surface 95. A base 94a of each spring 94 is attached to the corresponding cage bar 96 of the cage 93. A tip 94b of each spring 94 protrudes from the cage bar 96 toward the corresponding roller 92. Thus, the spring 94 can elastically push the roller 92.
As described above, besides the recess-shaped cam surfaces 95, the recessed portions 99 are formed on the outer periphery of the inner ring 90 so that the protruding portions 98 of the cage 93 allowing suppression of a variation in the distance L of the spring area are fitted in the respective recessed portions 99. However, each cam surface 95 is formed in an area that is different from the area of the corresponding recessed portion 99 and that is located away from the recessed portion 99 in the circumferential direction. Thus, in addition to a dimensional error in the cam surface 95 itself and a dimensional error in the recessed portion 99 itself, a dimensional error concerning circumferential arrangement of the cam surfaces 95 and the recessed portions 99 is likely to occur. Consequently, even when the protruding portions 98 of the cage 93 are fitted in the respective recessed portions 99 to allow the cage 93 to be positioned by the inner ring 11, the distance L of the spring area varies within the one-way clutch as in the above-described case. As a result, a heavy load is imposed on some of the springs 94, making the one-way clutch less durable (shortening the life of the one-way clutch). In particular, when the one-way clutch is provided in an alternator, the pulley (outer ring 91) rotates at high speed and involves significant and frequent rotational fluctuations, making the springs 94 likely to fatigue.